Saturday, June 24, 2017

The Nocturnal Sun

Waves Above the Earth May Have Once Caused a ‘Nocturnal Sun’

Airglow, light more than 60
miles above Earth’s surface, happens when molecules broken apart by
ultraviolet light from the sun reunite, releasing energy in the form of
light.Credit
NASA

It
was night, but people could see, almost as if it was day. There were no
streetlamps, no flood lights, no candles, sun or moon. But they could
read documents, make out pebbles on the ground and spot details of
landscapes hundreds of yards away. Distant mountains were illuminated.
Some called it the nocturnal sun.

Reports
of observations like these, dating to ancient Rome, have long perplexed
scientists and onlookers. Scientists in Canada may have an answer.In a study published this week in Geophysical Research Letters, Gordon Shepherd and his colleague Young-Min Cho, atmospheric scientists at York University, explain how waves inEarth’s atmosphere may have made these ancient bright nights possible.

Bright swaths of red in the
upper atmosphere, known as airglow, are seen in this image taken from
the International Space Station.Credit
NASA

A bright night starts with a dull light called airglow, which is found more than 60 miles above the earth’s surface. Normally, Earth’s atmosphere is made up mainly of nitrogen and oxygen, in their molecular forms.
That just means that rather than a single atom of oxygen, for example,
two of them are stuck together. But up in those heights, ultraviolet
light from the sun separates the atoms in these molecules. At night,
when the sun is gone, they come back together, releasing energy as they
reunite.

This energy is visible as light, and the presence of oxygen,
which they focused on in the study, can make it appear green. Scientific
instruments are sensitive enough to detect it, but not human eyes —
until a bright night, when an unexpected alignment of waves in our upper
atmosphere amplify that once invisible airglow, making it much
brighter.

These
waves, called zonal waves, are influenced by severe weather on Earth’s
surface and travel around the upper atmosphere. Dr. Shepherd and Dr. Cho
zeroed in on four kinds of zonal waves using images taken from a
satellite deployed in the 1990s to measure airglow and other features of
the atmosphere.

Usually,
the waves peak in different places along their journeys around Earth.
But “every once in awhile, the waves end up in the same spot,” said Dr.
Shepherd. “Just imagine waves in the ocean piling up together. That
makes a bigger wave.” And when they superimpose like that, the intensity
of the airglow increases so much, it’s possible for the naked eye to
see it, and may explain those nocturnal suns of the past.

Once
superimposed, the waves will stay that way for a while because they
move so slowly, said Dr. Shepherd, so bright nights will last two to
four nights. And, according to his analysis of the satellite images, one
bright night can shine over areas as big as Europe.

In
historical reports, people did not really mention what was going on in
the sky, said Dr. Shepherd. “They were just aware that suddenly they
could see things in their environment.”

With
so much light polluting our nights now, it is nearly impossible to make
out a bright night when it occurs in most places, let alone find a
photograph of one. When many of the observations took place, cameras
weren’t yet invented. And a photograph from Earth of the bright sky at
night wouldn’t be that impressive, said Dr. Shepherd. It’s something to
experience firsthand.

And
to do that requires patience, luck and a very special place. The
weather patterns that produce the waves leading to bright nights tend to
favor middle latitudes. “If you pick one location, like New York City,
it would only happen about once a year,” said Dr. Shepherd. And even
then, you’d need a clear night and no light pollution.

“We
have animal species that are disappearing. We have glaciers that are
disappearing. And bright nights too are disappearing, because there are
so many city lights everywhere,” said Dr. Shepherd. “There are going to
be fewer and fewer places where people can see them, and if they did,
they’d have to wait a long time.”

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This is a blog about what interests me. Here you will find stories on animals, including animal rights material, cute stuff, and random informative posts about weird, beautiful and interesting creatures. Horses, Spotted Hyenas, and Border Collies will make regular appearances.
Also prominently featured will be posts about the Arts. Animation, photography, and the traditional forms, plus "outsider art," film and books.
Other things that will surface here are Japan & the Japanese, John Oliver, surfing, skateboarding and My Little Pony: Friendship Is Magic, interesting places and structures,and my own art, writing and photography.
There will be rants. It's an election year, and I am beginning to have a political dimension to my personality. I am also horrified at the level of injustice and violence visited upon people here in the US and elsewhere - particularly against people of color, immigrants, and the LGBT community. Some of these stories will be very hard to read, but I believe we must read them to keep ourselves mindful of the racist and vicious things that happen every day, to speak out when we see discrimination, and root out its evil from ourselves.